1. Field of Invention
The present invention relates to a method for forming a semiconductor device. More particularly, the present invention relates to a method for forming an opening in a semiconductor device.
2. Description of Related Art
The conventional method for forming an opening in a semiconductor device includes the following steps. A photoresist layer is formed on a material layer. Then, the photoresist layer is patterned by the photolithographic process. An etching process is performed to form an opening in the material layer with the patterned photoresist layer.
As the shrinkage in the size of the semiconductor device, the control of critical dimension (CD) in the photolithographic process is the bottleneck in the process due to the limitation of light resolution and depth of focus (DOF). This bottleneck in the photolithographic process limits the formation of a small-size opening. Even with some advance technology such as phase shift mask (PSM), it is still difficult to form a small-size opening.